In general, laser trimmable components are formed as an individual trimmable unit that is formed or directly connected to a printed circuit board. Alternatively, laser trimmable components can be encapsulated in a hybrid circuit.
If the laser trimmable component is an individual component that is directly connected to a printed circuit board, valuable circuit board real estate must be used which in certain circumstances may be unacceptable.
In contrast, hybrid circuits have the advantages of reducing circuit board real estate as a number of components can be incorporated onto a thin or thick film substrate which can be mounted normal to the plane of the circuit board to thereby save space. The trimmable components on the substrate are trimmed before all components of the hybrid circuit are encapsulated in an epoxy coating. Unfortunately, due to tolerances of components on the circuit board, the pre trim values of the laser trimmable components of the hybrid circuit may be inadequately calibrated and in situ fine trimming of these components is generally not possible as they are encapsulated in the epoxy coating. This therefore requires the complete hybrid circuit to be removed and replaced with another hybrid circuit in the hope that the trimmable values may be adequately calibrated for use with the non-trimmable components mounted on the circuit board.